Switchable roller finger followers are known. See, for example, U.S. Pat. No. 7,174,869. Such finger followers have a secondary lever in the form of an outer lever pivotably mounted outside a primary lever in the form of an inner lever and a roller rotatably mounted on a transverse axle in a slot in the inner lever. The top surface of the outer lever can act as a contact surface for a high lift cam and the top surface of the roller acts as a contact surface for a low lift cam. A coupling element is mounted at one end of the finger follower and oil from an oil source is used to activate the coupling element. When the coupling element is activated, it locks the outer lever to the primary or in this case inner lever and requires the follower to follow the high lift cam and transfer the lift to the valve stem of an associated intake or exhaust valve. When the coupling element is deactivated, the secondary or in this case outer lever is free to pivot relative to the inner lever and, under the aid of a lost motion spring, the outer lever pivots freely in conjunction with the high lift cam while the motion of the low lift cam is transferred by the inner lever to the valve stem. This movement by the outer lever is conventionally referred to as the lost motion stroke.
Alternatively, the switchable finger follower can have a lift mode and a no lift mode. In this case, the secondary lever in the form of an inner lever is pivotably mounted within a primary or in this case outer lever, and a roller is rotatably mounted on a transverse axle in a slot in the inner lever. In the lift mode, a coupling device locks the secondary or in this case inner lever to the primary, outer lever so that the cam movement is transferred from the roller to the inner lever/outer lever which act as one piece and transfer the lift to a valve stem. In the no lift mode, the secondary or in this case inner lever is unlocked from the primary, outer lever and, under the aid of the lost motion spring, the secondary, inner lever is free to pivot relative to the primary, outer lever so that no lift is transferred.
In either case, the lost motion spring is used to absorb motion of the secondary lever relative to the primary lever to maintain contact between the cam follower of the secondary lever and the cam during the lost motion stroke. The size of the lost motion stroke available is often limited by the space available about the roller axle, as well as the angular displacement of the lost motion spring acting between the primary lever and the secondary lever. Additionally, the ends of the lost motion springs that contact the lost motion part require a high pre-load in order to prevent pumping up of the hydraulic lash adjuster support assembly out of its support opening in the block or head due to the oil pressure exceeding the downward spring pressure.
It would be desirable to provide a finger follower of the type noted above that would allow for lower preloads of the lost motion spring as well as smaller angular displacements, while still allowing the same or even greater lost motion travel between the inner and outer levers.